Welcome to my very own Quick References! This page lists commands, queries and code snippets I have trouble remembering. So rather than Google the same thing over and over, I write them down here.
Sources are provided whenever possible.
Link to section Bash
Link to section Check if environment variable is set
if [[ -z ${SOME_PATH+x} ]]
then
echo "SOME_PATH is not set!"
exit 1
fi
Link to section CSS
Link to section Reverse order of children on mobile
@media screen(max-width: 576px) {
.parent {
display: flex;
flex-direction: row-reverse;
}
}
Link to section EXIF
Link to section Update pictures’ date/timezone
I often forget to update my camera’s clock on date time savings and when I spend holidays on another timezone, so here are some commands to fix this.
# Remove an hour
exiftool "-DateTimeOriginal-=1::" .
# Add an hour
exiftool "-DateTimeOriginal+=1::" .
Note that by default, it will keep the original file, renamed DSCXXXXX_original.jpg. If you do not want to keep the
original file, add the -delete_original flag.
Link to section Git
Link to section Remove tag from origin
git push --delete origin YOUR_TAG_NAME
Link to section Java
Link to section JPA
Link to section Maintain order in list
Add the @OrderColumn annotation on the List. For example:
@Entity
@Table(name = "cats")
public class Cat {
@ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST, CascadeType.DETACH})
@OrderColumn(name = "priority")
@JoinTable(name = "cat_owner_list",
joinColumns = @JoinColumn(name = "cat_id"),
inverseJoinColumns = @JoinColumn(name = "owner_id")
)
private List<Owner> owner;
}
Link to section Javascript
Link to section Angular
Link to section Wait for user to stop typing before validating input
this.formGroup = this.fb.group({
'password': [ '', [ Validators.required ] ]
});
this.formGroup.get('password').valueChanges
.pipe(
debounceTime(500),
distinctUntilChanged())
.subscribe(() => {
this.formGroup.get('password').setValidators([
Validators.required,
this.validators.password
]);
this.formGroup.get('password').updateValueAndValidity();
});
Link to section Insert script programmatically
/* app.component.ts */
export class AppComponent implements OnInit {
constructor(
private _renderer: Renderer2,
@Inject(DOCUMENT) private _document: Document) {}
ngOnInit() {
const scriptEl = this._renderer.createElement('script');
this._renderer.setAttribute(scriptEl, 'async', '');
this._renderer.setAttribute(scriptEl, 'src', environment.scriptToInsert);
this._renderer.appendChild(this._document.body, scriptEl);
}
}
Link to section jq
jq is an utility to parse, query and manipulate JSON files directly from the shell
Link to section Order keys alphabetically
$ echo '{ \
> "d_key": "thingsome", \
> "a_key": "some value", \
> "c_key": "other value", \
> "b_key": "something" \
> }' | jq --sort-keys .
{
"a_key": "some value",
"b_key": "something",
"c_key": "other value",
"d_key": "thingsome"
}
Link to section Add field to an object
$ echo '{"foo": "bar"}' | jq '. + { "key": "value" }'
{
"foo": "bar",
"key": "value"
}
Link to section Add data to a field
$ echo '{ "key": "foo" }' | jq '.key += "bar"'
{
"key": "foobar"
}
Link to section Add data to array
$ echo '{
> "array": [
> "value1",
> "value2"
> ]
>}' | jq '.array += ["some value"]'
{
"array": [
"value1",
"value2",
"somevalue"
]
}
Link to section Filtering
$ echo '[ \
> { "id": 1, "name": "one" }, \
> { "id": 2, "name": "two" }, \
> { "id": 3, "name": "three" }, \
> { "id": 4, "name": "four" } \
> ]' | jq '.[] | select(.id % 2 == 0) | .name'
"two"
"four"
Link to section Array length
$ echo '[ \
> { "id": 1, "name": "one" }, \
> { "id": 2, "name": "two" }, \
> { "id": 3, "name": "three" }, \
> { "id": 4, "name": "four" } \
> ]' | jq '. | length'
4
Link to section Make a array out of a text file
$ cat file.txt
aaa
bbb
ccc
# input / "\n" is akin to input.split("\n") in most programming language
$ jq -Rsn '{ "array": (inputs / "\n" | select(lenght>0))}' < file.txt
{
"array": [
"aaa",
"bbb",
"ccc"
]
}
Link to section Assign value to bash script variable
variable=$( cat input.json | jq -r '.key' )
Link to section PostgreSQL
Link to section Duplicate a database
CREATE DATABASE newdb WITH TEMPLATE originaldb OWNER dbuser;
Link to section Disconnect every user from database
SELECT pg_terminate_backend(pg_stat_activity.pid) FROM pg_stat_activity
WHERE pg_stat_activity.datname = 'originaldb' AND pid <> pg_backend_pid();
Link to section List blocking requests
select pid,
usename,
pg_blocking_pids(pid) as blocked_by,
query as blocked_query
from pg_stat_activity
where cardinality(pg_blocking_pids(pid)) > 0;
Link to section Dynamic Interval
select now() + interval '1 day' * a.number_of_days from a;
Link to section Duration between two dates
SELECT
AGE('2012-03-05', '2010-04-01'),
DATE_PART('year', AGE('2012-03-05', '2010-04-01')) AS years,
DATE_PART('month', AGE('2012-03-05', '2010-04-01')) AS months,
DATE_PART('day', AGE('2012-03-05', '2010-04-01')) AS days;
Link to section Get the minimum / maximum value between fields
Use the LEAST(values...) and GREATEST(values...) functions.
Link to section Python
Link to section JSON array to CSV
import json
import os
# Open JSON file and load its content as dict
with open("input.json", encoding='utf-8') as json_data:
input = json.load(json_data)
json_data.close()
# Write headers
csv_rows = ["id,timestamp,method,path,responseCode,responseTimeMillis"]
# For each entry in the JSON array, insert a new line
for obj in input:
source = obj['_source']
csv_rows.append(f"{obj['_id']},{source['@timestamp']},{source['method']},{source['path']},{source['responseCode']},{source['responseTimeMillis']}")
# Convert array to text
array_as_string = "\n".join(csv_rows)
# Write CSV
filename = 'output.csv'
os.makedirs(os.path.dirname(filename), exist_ok=True)
with open(filename, "w+") as file
file.write(array_as_string)
Link to section SQL
Link to section Update table using data from another
UPDATE
Table_A
SET
Table_A.col1 = Table_B.col1,
Table_A.col2 = Table_B.col2
FROM
Some_Table AS Table_A
INNER JOIN Other_Table AS Table_B
ON Table_A.id = Table_B.id
WHERE
Table_A.col3 = 'cool'
Link to section Unix
Link to section Extracting text from multiple files using a regex
for file in $(find changes -type f -iname "*.xml"); do cat "$file" | perl -wne '/dropTable tableName="([a-z_]*)"/i and print "$1\n"' >> ~/Documents/dropped.txt; done
Link to section Listing lines that are in both or only one of two files
Print only lines common to both files
comm -12 file1.txt file2.txt
Get lines only found in first file
comm -23 file1.txt file2.txt
Get lines only found in second file
comm -13 file1.txt file2.txt
Note: comm requires both files to be sorted alphabetically (you can use sort).
Link to section Find text present in every files in a folder
grep -r --include "*.txt" texthere .
And to exclude directories from the search:
grep -r --include "*.json" --exclude-dir "dist" --exclude-dir "node_modules" texthere .
Link to section Finding process listening on specific port
sudo apt install net-tools
netstat -lnp | grep -w ':80'
Link to section Batch convert TIFFs to JPEGs
for f in *.tif; do echo "Converting $f"; convert "$f" "$(basename "$f" .tif).jpg"; done
Link to section Extract sub-folder content within a zip
unzip -j archive.zip 'folder/to/extract/*' -d 'where/to/extract/to/'
Link to section Wordpress
Because sometimes you gotta help someone using Wordpress.
Link to section Array structure
a:3:{i:0;s:3:"cat";i:1;s:6:"potato";i:2;s:40:"Friends don't let friends use Wordpress";}
a: array’s lengthi: item’s index in arrays: item’s length
Link to section List and update active plugins
SELECT option_value from prefix_options where option_name = 'active_plugins'
To disable a faulty plugin, edit the array as described in Array structure. Do not forget to update each following items’ indexes as well as the array size!